1. Field of the Invention
The present invention relates generally to a uni-body frame subassembly for a motor vehicle having a towing hitch. More specifically, it relates to a configuration for neutralizing the effect of a rear impact involving the rear bumper and a towing hitch member.
2. Background Art
Conventional uni-body frame assemblies and subassemblies for motor vehicles having a towing hitch member have been evolving for quite some time. Many automotive manufacturers attach a towing hitch member to a transverse member or rear bumper beam. The towing hitch member commonly extends below the frame or underbody of the vehicle and additionally may be the rearmost component on the vehicle. The lowered position of this towing hitch member creates a moment arm and can become particularly disadvantageous in a rear crash event.
The automotive industry has recently implemented longitudinal rear frame rail subassemblies having a convoluted shape. In response to an impact, the convoluted shape ideally causes the longitudinal rear frame rails to axially collapse in a controlled manner. In comparison to a conventional collapse of rear frame rails without a convoluted shape, this type of collapse absorbs a greater portion of the energy originating from a crash impact.
A partial or direct impact on the towing hitch member and/or rear bumper member can lead to a considerable moment on the rear vehicle subassembly. This moment commonly causes the rear bumper to aggressively rotate into the rear frame rails. This in turn causes the rear frame rails to fold abruptly in a localized spot and transmit a significant force to vehicle occupants. This motion eliminates the functionality of the convoluted shape in the frame rails, and thus the convoluted shape does not dissipate energy as intended.
The deficiency with most existing rear vehicle assemblies and subassemblies having the towing hitch member regards counteracting this moment caused by the placement of the towing hitch member in combination with a rear impact. While these vehicles may or may not include features for dissipating energy along the length of the vehicle, absorbing this moment is critical to the safety of vehicle occupants. Ideally, a rear vehicle subassembly would include features to absorb this moment in addition to facilitating an axially controlled collapse wherein energy is absorbed along the length of the vehicle.
Consider U.S. Pat. No. 6,814,379 to Shape Corporation which has an elaborate egg crate design intended to absorb energy upon impact. This rear vehicle subassembly, in addition to associated manufacturing costs, does not properly address or intend to counteract the moment which can occur upon an impact to a lowered towing hitch member. U.S. Pat. No. 6,896,303 to Mohr includes energy absorbing features directly within and around the towing hitch member. While these features may absorb energy along the length of the vehicle, they neglect to counteract the moment which occurs upon an impact to a lowered towing hitch member.
Another complication in the automotive industry involves providing uni-body constructed vehicles with adequate towing capacity. Without a frame spanning the length of the vehicle, many uni-bodies lack the strength and reinforcement needed to achieve credible towing capabilities.
Accordingly, there is an inherent need for a rear vehicle subassembly which overcomes the deficiencies in rear vehicle assemblies and subassemblies involving a towing hitch member.